The invention relates to a welding sleeve of thermoplastic material for joining tubular thermoplastic parts.
Welding sleeves are known (for example in U.S. Pat. No. 3,943,334) which have one or two heating zones of a spiral heating coil for joining two tubular plastic parts. Each heating zone has a uniform heating capacity over its length. Since the heat loss at the ends of each heating zone due to heat emission to the edge zones of the sleeve body is greater than the center region of the welding zone, the temperature distribution is irregular which is disadvantageous for satisfactory welding. Either overheating with damage to material may occur in the center region of the welding zone, or unsatisfactory welding may be
produced at the ends of the heating zone.
It is the principle object of the present invention to provide a welding sleeve of the above type whose heating coil is designed for uniform heat distribution in the one or more than one heating zone to achieve satisfactory welded joints.